While it is well known that multimorbidity is common and on the rise, the exact extent of the problem and the rate at which it is growing is not understood. It is reported to affect anywhere between 13-95% of patients globally, a range so wide that it indicates just how little is known about this global burden. The causes of multimorbidity are poorly understood and strategies for its prevention are lacking.

The report, produced by a working group of 17 international health experts, is the first to address the problem of multimorbidity on a global scale and highlights the inadequacy of the evidence required to guide health policy and medical practice. The project was supported in part by the UK Department for Business, Energy and Industrial Strategy.

Most health services, including the NHS, are not designed to care for patients with multiple illnesses. This is likely to contribute to the increasing pressures on health systems and budgets worldwide, the report suggests. It concludes that without a better understanding of multimorbidity, it will not be possible for any country to plan future healthcare resources and redesign services effectively.

Health conditions that frequently group together include heart disease, high blood pressure, diabetes, cancer, depression, anxiety, chronic obstructive pulmonary disease (COPD) and chronic kidney disease. However, it is unclear why some of these conditions cluster together, making it difficult to predict which patients may be most in need of preventive steps or increased care.

Evidence suggests multimorbidity is most common in women and people with low income, and is increasingly common in young people as well as in older people.

“While we know multimorbidity is very common, we don’t know precisely how many people live with multiple serious illnesses. From what we do know, I estimate tens of millions of Britons suffer from multimorbidity, and globally the number could be a billion. Similarly, while we know multimorbidity is increasing, we don’t know how quickly or which groups are experiencing the biggest increases.

“This report should be the tipping point of recognising that multimorbidity is an enormous threat to global health. It is a priority to get the evidence we need to develop effective strategies for prevention and treatment.”

The scientific community does not have an agreed definition of multimorbidity, which has hindered essential research needed to improve prevention and treatment. The report provides a new definition of multimorbidity and recommends that this be adopted by researchers globally.

Physical and mental health conditions often cluster together. Poor mental health can negatively affect quality of life and life expectancy more so than having multiple physical illnesses. The report highlights evidence that mental health conditions can lead to reduced physical health and vice versa. For example, type 2 diabetes has been reported to increase the risk of depression, and adults with depression are 37% more likely to develop type 2 diabetes. However, the division between health services treating mental and physical health often means that patients suffering from both physical and mental conditions are at particular risk of poor care.

Professor Stephen MacMahon added:

“How to prevent and manage multiple diseases is a challenge that GPs face every day, yet we have almost no evidence on which to provide guidance as to how to do this most effectively.

“We are facing a tidal wave of patients living with multiple long-term health conditions, and our report demonstrates how little we know about how to manage this. Outcomes appear to be worse in these patients and yet there is growing evidence that people with multimorbidity are less likely to receive appropriate care for the individual diseases they have. We face a situation where those in greatest need are least likely to receive appropriate care.

“For too long we’ve focussed almost exclusively on the management of single diseases, such as cancer and HIV. This means we have neglected the reality that most people with any one long-term disease typically have others.”

Professor Sir Robert Lechler PMedSci, President of the Academy of Medical Sciences said:

“People living with more than one illness often have more medical appointments and medications to manage, and doctors can struggle to balance their care. The toll of this can have a big impact on the quality of life of patients and their families.

“Multimorbidity is not an intangible problem. Research can give us the evidence needed to tackle this major health challenge and improve patients’ lives across the globe.

The report suggests tackling multimorbidity will be essential to reach the Sustainable Development Goals set out by the United Nations, and to progress towards the WHO framework on ‘integrated people-centred’ health services.

“Hundreds of millions of Chinese people are living with more than one long-term illness, and the problem is growing larger with more and more people living longer into old age. Having multiple illnesses increases the risks of dying, reduces levels of activity and wellbeing, and introduces a greater likelihood of missing medications or for drugs to interact with one another.

"However, as health services are conventionally organised around single disease areas, people with multiple illness have to see lots of doctors for different reasons which adds complexity, costs and problems with communications. Innovative integrated solutions such as increasing the skills of doctors in primary health care, use of digital health and electronic communications systems are required.”